An electric motor armature is usually made of a stack of metal laminations mounted on the motor shaft. The armature windings are wound on the lamination. Sometimes the laminations become loose on the shaft; sometimes the laminations separate slightly over time. As a result of one or both, the motor may become noisy or develop slight vibrations, or the armature connections may break at the commutator riser.
Armature repair can be difficult and expensive. The motor may be out of use for a considerable period of time. Sometimes the armature has to be replaced, if it cannot be disassembled, rewound, and then reassembled easily or inexpensively. It can be advantageous, for instance, with elevators, to be able to make these repairs in the field, to minimize cost and inconvenience.